The present invention relates to a method of examining and/or modifying surface structures of a sample by means of a beam impinging on the surface structure of the sample, in the case of which gas is supplied at least in the area of impingement of the beam on the surface structure of the sample.
From the technical publication W. H. Brunger and K. T. Kohlmann, xe2x80x9cE-Beam Induced Fabrication of Microstructuresxe2x80x9d, Micro Electro Mechanical Systems ""92, published in connection with the conference of the same name held in Travemxc3xcinde on Feb. 4 to 7, 1992, it is already known to produce microstructures on the basis of an electron beam-induced manufacturing method. For such a method, a modified scanning electron microscope is typically used for electron beam-induced deposition. The sample to be processed is arranged in a chamber in the area of impingement of the electron beam, the sample being surrounded by a metallo-organic precursor gas which is kept in the interior of a subchamber at a pressure of e.g. 2xc3x9710xe2x88x922 mbar. The electron beam enters the subchamber through an opening the subchamber maintaining the basic pressure within the microscope at 10xe2x88x925 mbar.
In order to obtain an increased deposition rate in the deposition process, this publication additionally suggests that a subchamber arrangement should be dispensed with and that the precursor gas should continuously be supplied to the point of impingement of the electron beam on the sample. In typical embodiments the continuous gas supply takes place via a gas nozzle having a small opening of e.g. 100 micrometers which is positioned very close to the point of impingement of the electron beam. Typical distances lie between 100 micrometers and 1 millimeter. This application of the precursor gas to a particular surface area of the sample, instead of flooding a subchamber or object chamber, has the advantage that the scattering of the beam is reduced, whereby the resolution is improved. However, even if the gas is continuously supplied to a particular surface area by means of a gas nozzle, the electrons or other image-forming particles of the beam will encounter gas particles on part of their way and will be scattered.
A further problem of the described deposition process by means of local application of gas to a surface area of the sample is that the deposition rate is limited by the gas flow, which, in turn, has an upper limit due to the maximum admissible chamber pressure of the system and the suction power of the pump system.
The publication D. Winkler, et al., xe2x80x9cE-beam Probe station . . . xe2x80x9d, Microelectronic Engineering 31 (1996), pp. 141-147, already discloses a method of electron-induced etching of passivated integrated circuits. In the case of this method, gas is supplied via a nozzle to the area of impingement of an electron beam on the surface structure to be etched. Etching gas molecules are here adsorbed on the surface, and a dissociation of the gas molecules takes place subsequently due to the interaction with the ion beam. Following this, product molecules with a substrate are formed, whereupon the etching product is desorbed and removed from the surface. Also during product formation, during desorption and during the removal of the etching product an interaction with the electron beam takes place.
However, the electron beam is, also in this case, scattered at the gas particles which are locally supplied via a nozzle to the surface structure of the sample to be etched.
Starting from this prior art, it is the object of the present invention to further develop a method of examining or modifying surface structures of a sample by means of a beam, in such a way that an improved resolution and/or an improved surface modification accuracy is achieved.
This object is achieved by a method according to claim 1.
The present invention is based on the finding that, in the case of the above-mentioned examination method or in the case of the method for modifying surface structures by means of a beam, an improved local resolution will be achieved when a discontinuous, preferably pulsed gas supply is used instead of the continuous gas supply.
According to one embodiment of the present invention, a gas blast of higher pressure is first applied to the surface of the sample. The gas particles are adsorbed on the surface where they remain for a certain period of time, which depends on the type of gas used and on the surface temperature of the sample, among other parameters. The particle beam will preferably be caused to impinge on the surface structure of the sample when, after the termination of the pulsed gas supply, the volume gas blasts are already rare, whereas the surface gas blasts still occur frequently, since the particles of the beam will then reach the surface unscattered where they will able to bring about chemical or other reactions.
The method is, however, also used for examining the surface of a sample by means of an electron beam; in this case, the discontinuously supplied gas serves to reduce or to prevent an electric charge on the surface of the sample.